grpctest: add example to show how it is used (#2552)

internal/grpctest/example_test.go

@@ -0,0 +1,61 @@
+/*
+ *
+ * Copyright 2019 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpctest_test
+
+import (
+	"testing"
+
+	"google.golang.org/grpc/internal/grpctest"
+)
+
+type s struct {
+	i int
+}
+
+func (s *s) Setup(t *testing.T) {
+	t.Log("Per-test setup code")
+	s.i = 5
+}
+
+func (s *s) TestSomething(t *testing.T) {
+	t.Log("TestSomething")
+	if s.i != 5 {
+		t.Errorf("s.i = %v; want 5", s.i)
+	}
+	s.i = 3
+}
+
+func (s *s) TestSomethingElse(t *testing.T) {
+	t.Log("TestSomethingElse")
+	if got, want := s.i%4, 1; got != want {
+		t.Errorf("s.i %% 4 = %v; want %v", got, want)
+	}
+	s.i = 3
+}
+
+func (s *s) Teardown(t *testing.T) {
+	t.Log("Per-test teardown code")
+	if s.i != 3 {
+		t.Fatalf("s.i = %v; want 3", s.i)
+	}
+}
+
+func TestExample(t *testing.T) {
+	grpctest.RunSubTests(t, &s{})
+}

internal/grpctest/grpctest.go

@@ -37,8 +37,15 @@ func getTestFunc(t *testing.T, xv reflect.Value, name string) func(*testing.T) {
 }
 
 // RunSubTests runs all "Test___" functions that are methods of x as subtests
-// of the current test.  If x contains Setup/Teardown functions, those are run
-// before/after each of the test functions, respectively.
+// of the current test.  If x contains methods "Setup(*testing.T)" or
+// "Teardown(*testing.T)", those are run before or after each of the test
+// functions, respectively.
+//
+// For example usage, see example_test.go.  Run it using:
+// $ go test -v -run TestExample .
+//
+// To run a specific test/subtest:
+// $ go test -v -run 'TestExample/^Something$' .
 func RunSubTests(t *testing.T, x interface{}) {
 	xt := reflect.TypeOf(x)
 	xv := reflect.ValueOf(x)